The most literal translation would be
Ruft nicht alle auf einmal.
But I wouldn't use a verb probably. I don't know why but that would sound unnatural or at least it doesn't sound ironic or funny anymore. Maybe it's just too long. Either way.. the thing that came to mind first was
Nicht alle auf einmal!
but there are other options, too, like
...

I'm not sure I ever heard a complete saying about this, but usually Germans will make a reference to the "Vorführeffekt" in a situation like this.
It pretty literally translates to *"demo effect" and means just that: that demonstrations in themselves have a tendency to go wrong.
Note that this also includes demonstrations of negative things, i.e. trying to ...

As always it depends on the context :)
If this relates to a thing (like a set of cards during a poker game)
Ist das alles, was du hast? / Mehr hast du nicht?
If this relates to a skill (like fighting) you would add drauf or können
Ist das alles, was du drauf hast? / Mehr kannst du nicht?
If this relates to a quantity (like the force of a punch)
...

I would use:
Geburtsname
for the original name as this is a legal term for a child's default surname (see § 1616 BGB). "Ursprünglicher Name" is okay, too.
For a newly adopted name changed later, I propose:
angenommener Name
(not sure whether translating this as "adopted name" is correct).
EDIT: AFAIK there's no fixed terminology for cases of ...

I'd probably say
Das ist doch keine Wissenschaft.
or
Das ist doch kein Hexenwerk.
LEO's forums contain a few more suggestions (e.g. here).
I wouldn't use Raketenwissenschaft or rocket science in German except when talking informally to peers of whom I know that they know English well enough.

Yes, those sentences are correct. Most used is the first sentence
Ich bin fast 18.
The other sentence sounds somewhat awkward. Beinahe has - imho - a connotation that means that there had almost something happened.
Beinahe hätte ich den Zug verpasst. (I almost missed the train.)
So, I'd recommend not to use beinahe.
A typical alternative is
...

Both Entschuldigung (which is a noun; it is an abbreviated form of ich bitte um Entschuldigung) and entschuldigen Sie can be used in a similar way to es tut mir leid; unlike it, they can also be used when interrupting someone:
Excuse me, what time is it?
Entschuldigung, wie spät ist es?
(Es tut mir leid, wenn ich störe, aber ... is also possible.)
...

There are some minced oaths in German as well, such as Scheibenkleister or Scheibenhonig. They might be less offensive than Scheiße (or Mist), and, at least in the case of "Scheibenhonig", might even help brighten up the general mood a bit.
Apart from that, Verflixt (und zugenäht [optional])! would be another not-quite offensive alternative I can think of ...

"Wie bitte?" or simply "Bitte?" is the standard polite form. "Was?" is also common, but shows bad manners. Use it only if you are sure the addressed person doesn't mind.
By the way, I would remove "Ich brauche eine Auskunft." from that list. Nobody talks like that.

In German it’s perfectly normal and not unfriendly to be direct, so why not keep it simple?
Bitte keine Geschenke!
I think the only way to really make this request more friendly would be by stating the reason for it.

In my experience "Mist" is not very offensive. Nobody would mind if you used it even in a business meeting or social event. In fact "Mist" is the least offensive real swear word that I can think of. But don't aggravate it further by adding "verfluchter/verdammter/elender Mist".
[So ein] Mist, ich habe meine Notizen zu Hause vergessen.
Variants to ...